The invention concerns a process for the preparation of a surface of a metal wall for the transfer of heat during the evaporation and condensation, respectively, of liquid and vapor phase media, respectively, preferably in heat-tubes. The invention equally concerns heat-tubes produced by the above-mentioned process.
It is known that roughening the surface of metal walls will improve their heat transfer properties. Thus, it has been proposed in DE-OS No. 25 46 444 to mechanically roughen a heat transfer wall for boiling liquids, to provide a plurality of so-called evaporation nuclei. Vapor bubbles will be formed on these locations when the boiling temperature is reached and thus the transfer of heat by such walls is improved. However, such a mechanical process is highly involved and expensive and in particular cannot be applied to inaccessible walls, for example, in tubes with small diameters. It is further known from DE-P No. 636 071, to etch the surface of tubes for the purpose of heat transfer in order to obtain a larger effective heat transfer surface. This measure is based on the fact that convective heat transfer is a function of the effective surface and the surface area can be increased by means of intensive and prolonged etching.
However, the increase in surface area obtained by etching in this manner does not take into account the peculiarities of heat transfer during changes in phase, i.e., during evaporation or condensation. During change of phase the formation of the so-called evaporation or condensation nuclei is of importance.